Posted
by
Zonk
on Thursday April 10, 2008 @03:41PM
from the hard-to-spot-with-all-the-space-dust dept.

mikkl666 writes "Following the recent story about the discovery of the youngest planet outside our solar system, Spanish researchers now report that they found the smallest exoplanet observed so far. The planet, known as GJ 436c, was found by analyzing distortions in the orbit of another, larger planet, and its radius is only about 50 percent greater than the Earth's. The scientists are confident that their new method will lead to a series of further discoveries: 'I think we are very close, just a few years away, from detecting a planet like Earth.' You can also reference the the original paper online for further details."

So you are saying that I can deduce a small child hovering around an obese parent by the way the bigger person's fat jiggles? Brilliant! Now if it only works on fat chicks, then I can discover if they have a hot, smaller female friend nearby...

Remember, if you hold density constant, an increase in radius translates to a power of three increase in volume, because it's expanding through three dimensions. A 50% increase in radius would result in a (1.5 ^ 3) 3.375 increase in mass. So, a five-fold increase in mass isn't that unreasonable; it's only a 48% increase in density. That's a lot, but you don't have to resort to white-dwarf style matter densities.

At 5x mass and 1.5x radius, I believe the surface gravity would only be about 2.2 g's.

At 5x mass and 1.5x radius, I believe the surface gravity would only be about 2.2 g's

This poses a question. Would rocket power be sufficient to get off a planet of this mass? On earth, it seems rockets are pushed to the limit to launch any significant payload. At twice earth gravity, it seems like your payloads would really be limited, if you can even reach escape velocity with rocket technology.

Well, besides humans, this would also aply to any intelligent life that might evolve on such a planet. Would rocket technology be sufficient to get off a planet with two or three times the gravity of earth? At point would the gravity be too great for rocket technology to work?

I'm sure we'd have no problem with that sort of technology by the time we actually reached that planet.

Well, that's sort of a meaningless answer, since your talking about technology that doesn't exist either in reality or in th

what is the minmum possible size/mass of a planet according to the new definition of 'planet'?

I don't know about that (well I do know but you could just look it up) but if a planet 4.7 times as heavy and 50% bigger than Earth was considered too small/lightweight to be considered a planet I'd seriously consider packing my bags and moving to a real planet like Uranus (to live in an airship of some sort that is, I'm very aware that you can't actually stand on Uranus, thank you!).

According to the IAU definition a planet needs to orbit around the Sun. No exoplanet is really a planet. Though the question depends a lot on what it's made of. It needs to be at hydrostatic equilibrium and fairly round (this is easier fluids and gases) and it needs to have cleared it's area.

Lets say it needs to be about the size of mercury and sweep the question under the rug as frankly a ball of water the size of a basketball, if the only object orbiting a star, would qualify as a planet.

Don't assume that intelligent life could only develop on a planet exactly like ours. Even just considering carbon-based life as we know it, life could still survive just fine [molvray.com] in a higher or lower gravity version of Earth. Lower gravity would likely mean a thinner atmosphere but oceans would still be habitable. Higher gravity would mean life forms couldn't grow as large on land. I don't think either of those would prohibit intelligent life from developing. And that's also assuming intelligent life just

There is the possibility that life has developed on a planet very different from our own. However, we know for certain that inteligent life can develop on a planet like ours. When dealing with finite resources you frequently get better results staying with the known.

I'm not arguing that SETI should avoid any solar system that wasn't identical to ours, but it is far more probably that inteligent life would develop on a planet similar to ours.A planet wouldn't have to be a mirror image of earth but there's

What they mean to say is that this seems to be the lowest mass planet found orbiting a main-sequence star.

It's also annoying that the press release quotes the radius of the planet (which cannot be measured, and is only an approximation based on guesses at density), when what they actually measured is the mass. Planetary densities vary widely; they have no idea what the radius is.

This, ladies and gentlemen is why people don't RTFA. There's much better and accurate information in the comments. Can this mean that if the mass is higher but the density much lower, there could be earth-class gravity there? Would sound like a pretty good start to me...

Yes, I wish we could score the article -1, Wrong. This is the smallest exoplanet discovered "around a Sun-like star". More details on this and previous discoveries can be found at the Bad Astronomy blog:

Using the known minimum mass of the previously detected Gliese 581 b, and assuming the existence of Gliese 581 d, Gliese 581 c has a mass at least 5.03 times that of Earth. The mass of the planet cannot be very much larger than this or the system would be dynamically unstable.

It seems like it may be a little premature to assume that the new planet is the smallest, even when comparing to planets around main-sequence stars.

I agree the radius is probably a made up number.

Scientist: "Assuming a density similar to earth's, the radius of the planet would be 50% greater than Earth's."

I thought they could approximate the radius pretty well based on the dimming the planet does to the star as it passes across it. This provided the orbital planes lines up right for our viewing. Or does this only apply to large planets?

Even worse than wrong the Reuters article neglects to tell the interesting story of how this planet was found. Or less optimistically why the authors think it's there.

Astronomers have used various methods to find extra-solar planets but the two most successful ones are the radial velocity method and the transit method.
The RV method can be described at looking at how the star wobbles as a planet moves around it. Transits are simply partial eclipses. As the planet moves in front of the star it blocks ou

Actually here are two problems as I see itI agree with your shielding, force field would become a must for several reasons like radiation.1. long range and real time sensory is a bigger issue. You are seeing things where they use to be, and moving that fast

Energy is the easy part, we continue to develop nuclear or work on antimatter. The size/mass of it wont matter once it is out of our gravity.

I think we wont get shielding or long range sensory till after we can create gravity(or anti gravity) with a fli

Do the math. About the only feasible designs for near C craft are ones that rely on being to scoop up interstellar hydrogen and use that. Even antimatter doesn't give you enough energy to be able to manage it.

Do you honestly believe that all technology either should develop "all at once" or should follow your chronology? Besides the point of looking deep into the space is not entirely to find a place for humanity to go. Just understanding the universe is a goal worth pursuing. At least that's how some other people view science and fortunately I should say.

Understanding is always good. But shouldn't we prioritize the research. The universe is so vast there is always a finite possibility of discovering earth like planets within finite time. When such a possibility already exists, it is worth investing in ways to actually make use of any such discovery.

If you look over the last twenty years in relation to human history (to say nothing of geological time frames) technology has developed all at once. There's a huge, nay exponential effect on technology of having near universal communications and access to knowledge content. If you scrape off the foam from the top of the Internet, there's an aweful lot of beer there. It's nearly instantaneous from that perspective.

I remember watching my Star Trek and seeing them fly their starships right up to star systems because that was the only way to explore them. Shit, I suppose you'd still have to put sats in orbit and probes on the surface to do detailed science but holy shit, detecting planets from lightyears away, even making guesses as to habitability by looking at star type, planetary orbit, even getting spectrographic readings from the atmosphere. I never would have believe it in a book. Yeah, hyperdrives I could buy but not this. Reality is stranger than fiction. Heh, it's just like all of the scifi guys assuming that ambulatory robots would be the easy part and making them think fast and speak well would be the tough part.

...I'm ok with the orbital period of five days, that can be determined by the wobble the planet imparts to the star as it orbits. My problem is, how do they tell its rotational period?Think about this for just a moment. Bright star, probably a hundred timed the diameter of the planet, and many thousands of times more luminous; assuming the planet is rocky (and barren, and a colouration about that of bleached tarmac), it'll have a reflectivity of about 15-20% (also known as albedo). Earth's blue-green marble

Here's your answer:
They can't actually see the planet itself, nobody's been able to directly image a planet in another solar system yet (this is something I hope to be working on in the next few years). What they can see in the case of Gliese 436 is that the light coming from the star "dips" in intensity a little on a regular basis. This is caused by the 'transit' of Gliese 436b, a neptune mass planet. Basically the planet blocks some light from the star and that is what we actually detect.
Also with th

I (and a group of people) am actually researching this system myself. We observed a transit of GJ436b on March 30, and we're reducing the data now.
I'd like to point out, however, this paper is NOT a discovery article. I read it in February (before it was published), and I've got it on my desk right in front of me. Basically, it PREDICTS that there MIGHT be a planet of said radius and mass in an orbit about twice as far out as GJ436b (a transiting hot neptune), but it also says that more study is needed to confirm the existence of this planet. What my study was trying to do was to show that there's a change in GJ436b's orbit caused by this new theoretical planet. So far, things look promising, but we haven't confirmed anything yet.

In case you haven't checked the reports, the scientists have not *seen* the object. Nor have they *seen* any of the other objects they so quickly claim are exoplanets.If all you know are its mass, or diameter, and perhaps its orbital period that is insufficient information to claim it is a "planet". It should be a very large artificial satellite.

The astronomers are operating off of an assumption that the universe is dead (and therefore natural). Ooopps, then we probably shouldn't be here... They need to

No, not a moon. I am merely saying that when you only know its mass (or diameter) and or perhaps its orbital period, its a leap to go claiming something is a "planet".Just FYI, the papers by Lineweaver's groups suggest that ~70% of the "Earths" in our galaxy are older than ours, some of them much much older. That leaves plenty of time for them to have developed the technology to disassemble and reassemble planetary sized masses (indeed if we develop robust nanotechnology in this century we will probably h

You, of course, are making the assumption that there is intelligent extraterrestrial life outside our solar system, a claim which is supported by NO physical evidence. On the other hand, astronomers know that something large is there. Models of star formation predict that planets will form naturally when stars form. I'm going to go ahead and apply Ocham's razor here:
1)Large mass perturbing/blocking light from star
2)Good reason to think that it's a planet
3)No reason to think that an alien civilization

I don't disagree other than from the perspective that Lineweaver's argument says we are the "young kids on the block". You have physicists scratching their heads left and right trying to explain another observation "dark matter" when that is what you would have lots of if advanced civilizations simply converted their stars to Matrioshka Brains (complex Dyson Shells). But doing so would involve many civilizations far more advanced than we are and the physicists don't want to go there... (lets make up some

If it were only my reasoning, I might be more willing to take the easy way out and say all masses orbiting other stars are dead planets. But doing so screams of requiring a good explanation for why we are the first and/or only advanced technological civilization in our galaxy. Without some of those on the table the puzzle seems to be missing missing more than a few pieces.

What we can know about extra solar planets currently is rather limited by having to use multiple methods for each characteristic. Mass and orbit are estimated from orbital perturbation, size is estimated by occlusion, chemistry by several optical methods, none highly precise.

It seems likely that the quality of observation will not improve until better optical observation is possible, such as space based or multi site terrestrial installations. Currently we are making educated guesses.